An electrophotographic light-sensitive material may have various structures depending upon the characteristics required or an electrophotographic process to be employed.
An electrophotographic system in which the light-sensitive material comprises a support having thereon at least one photoconductive layer and, if necessary, an insulating layer on the surface thereof is widely employed. The electrophotographic light-sensitive material comprising a support and at least one photoconductive layer formed thereon is used for the image formation by an ordinary electrophotographic process including electrostatic charging imagewise exposure, development, and, if desired, transfer.
Furthermore, a process using an electrophotographic light-sensitive material as an offset master plate precursor for direct plate making is widely practiced. Particularly, a printing system using a direct electrophotographic printing plate has recently become important for providing high quality prints of from several hundreds to several thousands.
Binders which are used for forming the photoconductive layer of an electrophotographic light-sensitive material are required to be excellent in the film-forming properties by themselves and the capability of dispersing photoconductive powder therein. Also, the photoconductive layer formed using the binder is required to have satisfactory adhesion to a base material or support. Further, the photoconductive layer formed by using the binder is required to have various excellent electrostatic characteristics such as high charging capacity, small dark decay, large light decay, and less fatigue due to prior light-exposure and also have an excellent image forming properties, and the photoconductive layer stably maintains these electrostatic properties to change of humidity at the time of image formation.
Further, extensive investigations have been made on lithographic printing plate precursors using an electrophotographic light-sensitive material, and for such a purpose, binder resins for a photoconductive layer which satisfy both the electrostatic characteristics as an electrophotographic light-sensitive material and printing properties as a printing plate precursor are required.
However, conventional binder resins used for electrophotographic light-sensitive materials have various problems particularly in electrostatic characteristics such as a charging property, dark charge retention, and photo-sensitivity, and smoothness of the photoconductive layer.
In order to overcome these problems, JP-A-63-217354 and JP-A-1-70761 (the term "JP-A" as used herein means an "unexamined Japanese patent application") disclose improvements in the smoothness of the photoconductive layer and electrostatic characteristics by using, as a binder resin, a resin having a weight average molecular weight of from 1.times.10.sup.3 to 5.times.10.sup.5) and containing an acidic group in a side chain of a copolymer or an acidic group bonded at the terminal of a polymer main chain thereby obtaining an image having no background stains.
Also, JP-A-1-100554 and JP-A-1-214865 disclose a technique using, as a binder resin, a resin containing an acidic group in a side chain of a copolymer or at the terminal of a polymer main chain, and containing a polymerizable component having a heat- and/or photocurable functional group; JP-A-1-102573 and JP-A-2-874 disclose a technique using a resin containing an acidic group in a side chain of a copolymer or at the terminal of a polymer main chain, and a crosslinking agent in combination; JP-A-64-564, JP-A-63-220149, JP-A-63-220148, JP-A-1-280761, JP-A-1-116643 and JP-A-1-169455 disclose a technique using a resin having a low molecular weight (a weight average molecular weight of from 1.times.10.sup.3 to 1.times.10.sup.4) and a resin having a high molecular weight (a weight average molecular weight of 1.times.10.sup.4 or more) in combination; JP-A-2-11766 and JP-A-2-34859 disclose a technique using the above described low molecular weight resin and a heat- and/or photo-curable resin in combination. These references disclose that, according to the proposed technique, the film strength of the photoconductive layer can be increased sufficiently and also the mechanical strength of the light-sensitive material can be increased without adversely affecting the above-described characteristics owing to the use of a resin containing an acidic group in a side chain or at the terminal of the polymer main chain.
However, it has been found that, even in the case of using these resins, it is yet insufficient to maintain the stable performance in the case of greatly changing the environmental conditions from high-temperature and high-humidity to low-temperature and low-humidity. In particular, in a scanning exposure system using a semiconductor laser beam, the exposure time becomes longer and also there is a restriction on the exposure intensity as compared to a conventional overall simultaneous exposure system using a visible light, and hence a higher performance has been required for the electrostatic characteristics, in particular, the dark charge retention characteristics and photosensitivity.
The present invention has been made for solving the problems of conventional electrophotographic light-sensitive materials as described above and meeting the requirement for the light-sensitive materials.
An object of the present invention is to provide an electrophotographic light-sensitive material having stable and excellent electrostatic characteristics and giving clear good images even when the environmental conditions during the formation of duplicated images are changed to a low-temperature and low-humidity or to high-temperature and high-humidity.
Another object of the present invention is to provide a CPC electrophotographic light-sensitive material having excellent electrostatic characteristics and showing less environmental dependency.
A further object of the present invention is to provide an electrophotographic light-sensitive material effective for a scanning exposure system using a semiconductor laser beam.
A still further object of this invention is to provide an electrophotographic lithographic printing plate precursor having excellent electrostatic characteristics (in particular, dark charge retention characteristics and photosensitivity), capable of reproducing faithful duplicated images to original, forming neither overall background stains nor dot-like background stains of prints, and showing excellent printing durability.
Other objects of the present invention will become apparent from the following description and examples.
It has been found that the above described objects of the present invention are accomplished by an electrophotographic light-sensitive material comprising a support having provided thereon a photoconductive layer containing an inorganic photoconductive substance and a binder resin, wherein the binder resin contains at least one graft type copolymer containing, as a copolymerizable component, at least one mono-functional macromonomer (M) having a weight average molecular weight of from 1.times.10.sup.3 to 2.times.10.sup.4 and comprising an AB block copolymer being composed of an A block comprising at least one polymerizable component containing at least one acidic group selected from --PO.sub.3 H.sub.2, --COOH, --SO.sub.3 H, a phenolic hydroxyl group, ##STR6## (wherein R represents a hydrocarbon group or --OR' (wherein R' represents a hydrocarbon group)) and a cyclic acid anhydride-containing group, and a B block containing at least one polymerizable component represented by the general formula (I) described below and having a polymerizable double bond group bonded to the terminal of the main chain of the B block polymer. ##STR7## wherein a.sub.1 and a.sub.2 each represents a hydrogen atom, a halogen atom, a cyano group, a hydrocarbon group, --COOZ.sub.2 or --COOZ.sub.2 bonded bia a hydrocarbon group (wherein Z.sub.2 represents a hydrogen atom or a hydrocarbon group); V.sub.1 represents --COO--, --OCO--, --CH.sub.2l1 OCO--, --CH.sub.2l2 COO-- (wherein l.sub.1 and l.sub.2 each represents an integer of from 1 to 3), --O--, --SO.sub.2 --, --CO--, ##STR8## (wherein Z.sub.1 represent a hydrogen atom or a hydrocarbon group), --CONHCOO--, --CONHCONH--, or ##STR9## and R.sub.1 represents a hydrocarbon group, provided that when V.sub.1 represents ##STR10## R.sub.1 represents a hydrogen atom or a hydrocarbon group.